chore: deprecate abcABG and readStr method

[stevenhua0320]

@sbillinge ready to review. Note that for readStr method since it is an inherited class method from Structure. We have done the deprecation for readStr there and so its test method. So we don't have to edit anything from test here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.99%. Comparing base (74683b6) to head (d09a89c).
⚠️ Report is 3 commits behind head on v3.4.0.

Additional details and impacted files

@@           Coverage Diff           @@
##           v3.4.0     #164   +/-   ##
=======================================
  Coverage   98.99%   98.99%           
=======================================
  Files          13       13           
  Lines        1988     1995    +7     
=======================================
+ Hits         1968     1975    +7     
  Misses         20       20           

Files with missing lines	Coverage Δ
tests/test_lattice.py	99.57% <100.00%> (ø)
tests/test_p_discus.py	98.85% <100.00%> (ø)
tests/test_structure.py	99.80% <100.00%> (+<0.01%)	⬆️
tests/test_supercell.py	97.95% <100.00%> (ø)

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[sbillinge]

@stevenhua0320 nicely done there.